Liquid crystal display device

ABSTRACT

A mobile phone is provided which includes a liquid crystal display device in which a front window and a touch panel are bonded together with an adhesive sheet, wherein a logo having plural layers is formed on a back side of the front window. A touch-panel flexible wiring substrate is mounted to the touch panel. A plane distance between an end portion of the plural layers of the logo and an end portion of the touch panel is set to greater than zero. With this configuration, it is possible to prevent a peeling stress on the adhesive sheet, even if a thickness of the adhesive sheet is smaller than the sum of a thickness of the touch-panel flexible wiring substrate and a thickness of the logo.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. application Ser.No. 12/763,450, filed Apr. 20, 2010, and which application claimspriority from Japanese Patent Application JP 2009-107678 filed on Apr.27, 2009, the contents of which are hereby incorporated by referenceinto this application.

FIELD OF THE INVENTION

The present invention relates to a liquid crystal display device, andmore particularly to a small display device having a touch panel and afront window provided in the interfacial surface of the display devicefor electronic devices such as mobile phones.

BACKGROUND OF THE INVENTION

In the liquid crystal display device, a TFT substrate has pixelelectrodes and thin film transistors (TFTs), and the like, arranged at amatrix form. A color filter substrate has a color filters arranged atpositions corresponding to the pixel electrodes of the TFT substrate.The TFT substrate and the color filter substrate are opposite to eachother with a liquid crystal interposed therebetween. In such aconfiguration, the liquid crystal display device forms an image bycontrolling the transmittance of light of the liquid crystal moleculesfor each pixel.

Liquid crystal display devices can be made small and thin, and are usedin a wide range of applications in mobile phones or other electronicdevices. Recently a wide variety of applications have been implementedin mobile phones. There is also a demand for input devices to have afunction allowing finger input through a touch panel, in addition to theconventional key-button operation. In this case, the touch panel ismounted on the side of the color filter substrate of the liquid crystaldisplay panel.

Meanwhile, in the liquid crystal display device, there is a strongdemand for reducing the thickness of the liquid crystal display panel,in addition to reducing the overall size of the set, while keeping acertain size of the screen. The thickness of the liquid crystal displaypanel is reduced by polishing the outside of the liquid crystal displaypanel after production of the liquid crystal display panel. A liquidcrystal display panel includes two glass substrates. One is a TFTsubstrate in which pixel electrodes, thin film transistors (TFTs), andthe like, are formed. The other is a color filter substrate in whichcolor filters are formed. The TFT substrate and the color filtersubstrate are standardized, for example, to 0.5 mm or 0.7 mm. It isdifficult to obtain such standardized glass substrates from a market. Inaddition, very thin glass substrates have a problem relating tomechanical strength and bending in the production process, leading to areduction in the production yield. As a result, the liquid crystaldisplay panel is formed by the standardized glass substrates, and thenthe outside of the liquid crystal display panel is polished to reducethe thickness of the liquid crystal display panel.

The reduction of the thickness of the liquid crystal display panel posesa problem of the mechanical strength. When a mechanical pressure isapplied to the display surface of the liquid crystal display panel,there is a risk that the liquid crystal display panel will be broken.This is the same for the touch panel set to the liquid crystal displaypanel due to a small thickness of the touch panel.

In order to prevent the liquid crystal display panel from being brokenby outside force, a front window of resin or glass is attached to thescreen side of the liquid crystal display panel. In this case, an airlayer exists between the liquid crystal display panel and the touchpanel, or between the touch panel and the front window. Thetransmittance of the light from the backlight is reduced by thereflection from the interface in this area.

In order to prevent this, JP-A No. 83491/2008 describes a configurationin which an adhesive layer or an anti-reflection coating is formedbetween the liquid crystal display panel and the touch panel, or betweenthe touch panel and the front window.

A liquid crystal display device having a liquid display panel, a touchpanel, and a front window, is often labeled with a logo representing theabbreviation of the phone function or the telephone service company.Such a logo is formed by printing on the back side of the touch panel.

The logo is displayed in white or a predetermined color. The display isformed by applying a predetermined color or white to a cut-out shape ofa predetermined logo printed in black. As a result, the thickness of therecoated portion of the logo is increased to about 20 μm.

The front window and the touch panel are bonded together with anadhesive sheet. If a thick printed mark is formed between the adhesivesheet and the front window, this will have an adverse effect on theadhesive force between the touch panel and the adhesive sheet. Thus, therecoated portion of the logo should be formed on the outside of theadhesive sheet.

A touch-panel flexible wiring substrate is connected to the touch panelin order to supply electric current and signals to the touch panel. Forthis reason, the adhesive sheet may not be provided in the vicinity ofthe area in which the touch-panel flexible wiring substrate is mounted.

However, when the recoated logo is formed as described above and isprovided on the outside of the adhesive sheet, the touch panel, thetouch-panel flexible wiring substrate, and the logo may overlap witheach other. The overlapping of the three components may cause a stresspeeling apart the front window and the touch panel. Such a stress has anadverse effect on the reliability of the liquid crystal display panel.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a liquid crystaldisplay device having a liquid crystal display panel, a touch panel, afront window, and a logo formed on the front window, with aconfiguration that ensures the reliability of the adhesive force betweenthe front window and the touch panel.

The present invention overcomes the problems identified above. Specificconfigurations are as follows.

(1) A liquid crystal display device includes a liquid crystal displaypanel with a backlight housed in a resin mold, a touch panel attached tothe liquid crystal display panel, and a front window attached to thetouch panel. The touch panel and the front window are bonded togetherwith an adhesive sheet. A touch-panel flexible wiring substrate isconnected to a specific side of the touch panel. A logo having plurallayers is formed on a surface of the front window on the side of thetouch panel. A portion of the logo corresponding to the plural layers isprovided on the outside of the adhesive sheet. A plane distance betweenan end portion of the plural layers of the logo and an end portion ofthe touch panel is greater than zero.

(2) In the liquid crystal display device described in (1), when athickness of the adhesive sheet is d1, a thickness of the portion of thelogo corresponding to the plural layers is d2, and a thickness of thetouch-panel flexible wiring substrate is d3, the relationship d1<d2+d3is established.

(3) In the liquid crystal display device described in (1), the planedistance between an end portion of the plural layers of the logo and anend portion of the touch panel is greater than 0.3 mm.

(4) A liquid crystal display device includes a liquid crystal displaypanel with a backlight housed in a resin mold, a touch panel attached tothe liquid crystal display panel, and a front window attached to thetouch panel. The touch panel and the front window are bonded togetherwith an adhesive sheet. A touch-panel flexible wiring substrate isconnected to a specific side of the touch panel. A logo is formed on asurface of the front window on the side of the touch panel. The logo isformed by two layers including a first layer and a second layer from theside of the front window. A portion of the logo corresponding to the twolayers is provided on the outside of the adhesive sheet. A planedistance between an end portion of the second layer of the logo and anend portion of the touch panel is greater than zero.

(5) A liquid crystal display device includes a liquid crystal displaypanel with a backlight housed in a resin mold, a touch panel attached tothe liquid crystal display panel, and a front window attached to thetouch panel. The touch panel and the front window are bonded togetherwith an adhesive sheet. A touch-panel flexible wiring substrate isconnected to a specific side of the touch panel. A logo is formed on asurface of the front window on the side of the touch panel. The logo isformed by three layers including a first layer, a second layer, and athird layer from the side of the front window. An end portion of thesecond layer is covered by the third layer. A portion of the threelayers of the logo is provided on the outside of the adhesive sheet. Aplane distance between an end portion of the second layer of the logoand an end portion of the touch panel is greater than zero.

According to the present invention, no peeling stress is applied to theadhesive sheet, even if the thickness of the adhesive sheet for bondingthe front window and the touch panel is smaller than the thickness ofthe touch-panel flexible wiring substrate and the thickness of the logoformed on the front window. As a result, it is possible to provide ahighly reliable liquid crystal display device.

Further, according to the present invention, the thickness of theadhesive sheet for bonding the front window and the touch panel can bemade smaller than the thickness of the touch-panel flexible wiringsubstrate and the thickness of the logo formed on the front window. As aresult, it is possible to reduce the thickness of the liquid crystaldisplay device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a liquid crystal display device according to afirst embodiment;

FIG. 2 is a top view of the liquid crystal display device in which atouch panel is mounted;

FIG. 3 is a view of the liquid crystal display device in which a frontwindow is mounted;

FIG. 4 is a cross-sectional view of FIG. 3;

FIG. 5 is an exploded perspective view of optical sheets;

FIGS. 6A to 6F are views of the process of forming a logo;

FIG. 7 is a detailed cross-sectional view around the logo;

FIGS. 8A, 8B, and 8C are views of the process of forming the logoaccording to a second embodiment;

FIG. 9 is a detailed cross-sectional view around the logo according tothe second embodiment; and

FIG. 10 is a detailed cross-sectional view around the logo according toa third embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present invention will be described in detail throughembodiments.

First Embodiment

FIG. 1 is a top view of a liquid crystal display device used for mobilephones or other electronic devices, according to the present invention.In FIG. 1, a color filter substrate 20 is mounted to a TFT substrate 10.A liquid crystal layer, not shown, is interposed between the TFTsubstrate 10 and the color filter substrate 20. The TFT substrate 10 andthe color filter substrate 20 are bonded together with a sealingmaterial, not shown, which is formed in the frame portion of the liquidcrystal display panel. The TFT substrate 10 is made to be larger thanthe color filter substrate 20. A terminal portion is formed in theportion of the TFT substrate 10 extending beyond the color filtersubstrate 20, in order to supply power, image signals, scan signals, andthe like.

An IC driver 30 is connected to the terminal portion to drive scanlines, image lines, and the like. The IC driver 30 includes a scan linedrive circuit and an image signal line drive circuit. The IC driver 30is supplied with scan signals and image signals through a main flexiblewiring substrate 40 connected to the terminal portion.

An upper polarization plate 21 is attached to the upper side of the TFTsubstrate 10. The overall size of the upper polarization plate 21 issubstantially equal to the display area. In other words, the liquidcrystal can only control polarized light, so that a lower polarizationplate is attached to the lower side of the TFT substrate 10 in order topolarize the light from the backlight into linearly polarized light. Thelinearly polarized light is modulated by the liquid crystal layer. Thetransmittance is changed for each pixel, and thus an image is formed.Then, the image is visible to human eyes when the light is polarized(analyzed) by the upper polarization plate 21.

The whole liquid crystal display panel is housed in a frame-like resinmold 60. The backlight described below is also housed on the lower sideof the liquid crystal display panel in the resin mold 60. In FIG. 1, themain flexible wiring substrate 40, which is connected to the terminalportion of the liquid crystal display panel, is folded over the backsurface in an end portion of the resin mold 60. In this way, the overallsize of the liquid crystal display device is reduced.

FIG. 2 is a view in which a touch panel 100 is bonded to the liquidcrystal display panel explained with FIG. 1. The touch panel 100 is madeto be slightly larger than the color filter substrate 20 of the liquidcrystal display panel, covering also a part of the resin mold 60. InFIG. 2, a touch-panel flexible wiring substrate 50 is mounted to an endportion of the touch panel 100 in order to supply power and signals tothe touch panel 100. The touch-panel flexible wiring substrate 50 isalso folded over the back surface in the end portion of the resin mold60, to reduce the overall size of the liquid crystal display device. Itshould be noted that the main flexible wiring substrate 40 and thetouch-panel flexible wiring substrate 50 are connected to each other onthe back surface of the resin mold 60.

In general, the substrate of the touch panel is formed by a glass.However, a plastic substrate may also be used if it is transparent andcan sustain anneal temperatures for ITO, and the like. Examples of thetransparent resin include acryl and polycarbonate.

The substrate of the touch panel 100 is attached to the color filtersubstrate 20 of the liquid crystal display panel with an adhesivematerial. In this embodiment, for example, an acrylic-based UV curableresin 110 is used as the adhesive material. The UV curable resin 110initially is a liquid. The liquid crystal display panel and the touchpanel 100 are bonded together in a reduced-pressure atmosphere,preventing air bubbles from entering.

The cured UV curable resin 110 is thermoplastic. In other words, this isbecause when defects such as air bubbles and foreign materials are foundbetween the touch panel 100 and the liquid crystal display panel afterthe completion of the bonding process, the touch panel 100 is detachedfrom the liquid crystal display panel for reproduction. It should benoted that an adhesive sheet can also be used to bond the color filtersubstrate 20 and the touch panel 100 together. In this case, theadhesive sheet is preferably also thermoplastic.

FIG. 3 shows a state in which a front window 200 is mounted to theliquid crystal display panel in which the touch panel 100 is mounted asshown in FIG. 2. In general, the front window 200 is formed by a glasswith a thickness of about 0.5 mm. Plastic such as acrylic resin andpolycarbonate resin can also be used as the material of the front window200.

When the front window 200 is mounted, the adhesive sheet 210 is providedbetween the touch panel 100 and the front window 200. In this case, theadhesive sheet 210 is formed on the side of the front window 200 to makethe operation easier. Further, the adhesive sheet 210 used here is alsothermoplastic by taking into account the possibility of reproducing thetouch panel 100, as in the case of the UV curable resin 110 formedbetween the liquid crystal display panel and the touch panel 100.

In FIG. 3, the overall size of the front window 200 is larger than theliquid crystal display panel and the resin mold 60, covering the entireliquid crystal display panel and the other components. Further, thefront window 200 also covers the main flexible wiring substrate 40mounted to the TFT substrate 10, as well as the touch-panel flexiblewiring substrate 50 mounted to the touch panel 100.

In FIG. 3, a logo 80 is provided on the back side of the front window200 in a peripheral portion thereof. The logo 80 is provided in aposition overlapping the touch-panel flexible wiring substrate 50.

FIG. 4 is a cross-sectional view taken along line A-A of FIG. 3. In thepresent specification, the combination of the TFT substrate 10 and thecolor filter substrate 20 is referred to as the liquid crystal cell.Further, a lower polarization plate 11 and an upper polarization plate21 are bonded to the liquid crystal cell, which is referred to as theliquid crystal display panel. The touch panel 100 is bonded to the upperpolarization plate 21 bonded to the color filter substrate 20 by meansof the UV curable resin 110.

On the touch panel 100, the front window 200 is bonded with the adhesivesheet 210. There may be a case in which the front window 200 is formedof plastic such as polycarbonate or acryl. The overall size of the frontwindow 200 is large, covering the touch-panel flexible wiring substrate50 as well as the main flexible wiring substrate 40.

The touch-panel flexible wiring substrate 50 is connected to the touchpanel 100. The touch-panel flexible wiring substrate 50 is provided withan electronic component 51 for the touch panel 100. The electroniccomponent 51 for the touch panel 100 is provided on the lower side ofthe flexible wiring substrate 50.

In FIG. 4, the IC driver 30 is provided in the terminal portion of theTFT substrate 10 of the liquid crystal cell. Further, the main flexiblewiring substrate 40 is connected to a terminal formed in the TFTsubstrate 10. The main flexible wiring substrate 40 is folded over theback surface of the liquid crystal display panel.

An LCD electronic component 41 is mounted to the main flexible wiringsubstrate 40. In FIG. 4, the front window 200 is designed to also coverthe LCD electronic component 41 mounted to the main flexible wiringsubstrate 40. It should be noted that the electronic component is notnecessarily mounted downward as shown in FIG. 4. The electroniccomponent may be provided upward in the portion of the flexible wiringsubstrate extending along the back surface of the backlight, dependingon the layout.

In FIG. 4, the electronic component is provided on the lower side of themain flexible wiring substrate 40. At the same time, a light emittingdiode 70 is also provided on the lower side of the main flexible wiringsubstrate 40 along with the other electronic component. However, thelight emitting diode 70 is provided in a portion of the main flexiblewiring substrate 40 folded over the back surface of the resin mold 60.In this way, the light emitting diode 70 can be housed in a concaveportion formed in the resin mold 60, when the main flexible wiringsubstrate 40 is folded over the back surface of the resin mold 60. Then,as shown in FIG. 4, the light emitting diode 70 is disposed opposite toan end of a light guide panel 62, which forms a part of the backlight.In this embodiment, a white light emitting diode is used as the lightemitting diode 70.

In FIG. 4, the liquid crystal display panel is placed on the resin mold60. The resin mold 60 is shaped like a rectangular frame. In FIG. 4, thelower polarization plate 11 of the liquid crystal display panel ishoused in the resin mold 60, and the backlight is provided on the backsurface of the lower polarization plate 11. The backlight has thefollowing configuration.

The light guide panel 62 is disposed at one end opposite to the lightemitting diode 70. The role of the light guide panel 62 is to direct thelight from the light emitting diode 70 entering from the side surface,towards the liquid crystal display panel. The size of the light emittingdiode 70 is large. For this reason, the thickness of the whole liquidcrystal display device is reduced by increasing the height of the lightguide panel 62 at the portion opposite to the light emitting diode 70,and by reducing the thickness at the portion overlapping optical sheetsdescribed below.

In FIG. 4, a reflective sheet 61 is provided on the lower side of thelight guide panel 62. This is in order to reflect and direct the light,which travels from the light guide panel 62 downward, towards the liquidcrystal display panel. Then, as shown in FIG. 5, optical sheets 67including a lower diffusion sheet 63, a lower prism sheet 64, an upperprism sheet 65, and an upper diffusion sheet 66, are provided on theupper side of the light guide panel 62.

FIG. 5 is an exploded perspective view of the optical sheets 67. In FIG.5, the lower diffusion sheet 63 has a role to reduce the variation inbrightness. The lower prism sheet 64 has a role to direct the lightspread in the a direction from the backlight, towards the liquid crystaldisplay panel. The upper prism sheet 65 has a role to direct the lightspread in the b direction from the backlight, towards the liquid crystaldisplay panel. The upper diffusion sheet 66 has a major role to reducethe occurrence of moire between the lower prism sheet 64 or the upperprism sheet 65, and the liquid crystal display panel.

Returning to FIG. 4, the optical sheets 67 are laminated on the lightguide panel 62. A distance of about 50 μm is provided between the upperdiffusion sheet 66 on the top of the optical sheets 67, and the lowerpolarization plate 11 of the liquid crystal display panel. This is toprevent scratches caused by friction between the lower polarizationplate 11 and the upper diffusion sheet 66.

In FIG. 4, the main flexible wiring substrate 40 connected to the liquidcrystal cell, and the touch-panel flexible wiring substrate 50 connectedto the touch panel 100 are both folded over the back surface of theliquid crystal display panel. The main flexible wiring substrate 40 andthe touch-panel flexible wiring substrate 50 are connected to each otherin a portion not shown in FIG. 4.

In FIG. 4, the logo 80 is formed by printing on the back side of thefront window 200 in which the adhesive sheet 210 does not exist. Thelogo 80 is provided in a position overlapping the touch-panel flexiblewiring substrate 50. The logo 80 is formed by plural layers. FIG. 4shows a cross section of the plural layers of the logo 80.

FIGS. 6A to 6F are views showing the method for forming the logo 80. Thelogo 80 is formed by printing. In FIGS. 6A to 6F, the logo 80 is formedof two layers. A first layer 81 is a black resin, in which a desiredmark to be displayed is formed by printing. In FIGS. 6A to 6F, the cutout of A, B, C, D is printed on the first layer 81. FIG. 6A is a viewseen from the front side of the front window 200. FIG. 6B is a view seenfrom the back side of the front window 200. The printing pattern is asshown in FIG. 6B. FIG. 6E is a cross-sectional view showing the state inwhich the first layer 81 of the logo 80 is printed.

The logo 80 is displayed in white or a predetermined color. This is byapplying a second layer 82 to the first layer 81. FIG. 6C is a view ofthe state in which the second layer 82 is applied to the first layer 81,as seen from the back side of the front window 200. As shown in FIG. 6C,the second layer 82 is applied to a portion of the first layer 81.

FIG. 6F is a cross-sectional view of FIG. 6C. In FIG. 6F, the secondlayer 82 covers a window portion of the first layer 81. The color of thelogo 80 is determined by the second layer 82. The second layer 82 isformed by a resin with a pigment of a predetermined color dispersedtherein. FIG. 6D is a view of the logo 80 formed as described above, asseen from the front side of the front window 200.

The logo 80 is supposed to be visually recognized by reflecting lightfrom outside. However, as shown in FIG. 4, the small liquid crystaldisplay device for electronic devices such as mobile phones uses a lightemitting diode as a light source. The light emitting diode should emitlight with high brightness. The light from the light emitting diodeleaks from the resin mold 60 or the optical components, and some of thelight reaches the lower part of the logo 80. When the light from thelight emitting diode has an effect on the logo 80, a predeterminedvisibility of the logo 80 may not be obtained.

In order to eliminate the effect of the light from the light emittingdiode on the visibility of the color or other optical characteristics ofthe logo 80, it is necessary to block the light from the light emittingdiode in the portion of the logo 80, or to increase the thickness of thesecond layer 82 of the logo 80. In this embodiment, the thickness of thesecond layer 82 is increased to remove the effect of the light from thelight emitting diode.

In FIG. 6F, the thickness of the first layer 81 of the logo 80 is about10 μm, and the thickness of the second layer 82 is about 15 μm or more.Thus, the thickness d2 of the second layer 82 of the logo 80 is 25 μm ormore. Reducing the thickness of the liquid crystal display device is arequirement for the use of mobile phones and other electronic devices.For this reason, increasing the thickness of the logo 80 may be aproblem.

FIG. 7 is a detailed cross-sectional view around the logo 80 of theliquid crystal display device shown in FIG. 4. In FIG. 7, the thicknessd1 of the adhesive sheet 210 is, for example, 100 μm. The thickness d2of the second layer of the logo 80 is, for example, 25 μm. The thicknessof the touch-panel flexible wiring substrate 50 is about 70 μm. In FIG.7, the d1 of the adhesive sheet 210 is slightly greater than the sum ofthe thickness d2 of the logo 80 and the thickness d3 of the touch-panelflexible wiring substrate 50.

However, taking into account the variation in the thickness of thecomponents, it is possible that d1 may be smaller than the sum of d2 andd3, namely, d1<d2+d3. In addition, the reduction in thickness is thetypical requirement for the liquid crystal display device, so that afurther reduction in the thickness of the adhesive sheet 210 may also beexpected. In this case, d1<d2+d3 may be normalized.

When the logo 80 is provided in the overlapping portion of the frontwindow 200, the touch-panel flexible wiring substrate 50, and the touchpanel 100 in the case in which d1<d2+d3 is established, a peeling stressis applied to the front window 200 and the touch panel 100 that arebonded together with the adhesive sheet 210. In FIG. 7, the first layer81 of the logo 80 extends below the adhesive sheet 210. The adhesivesheet 210 is flattened and the thickness of the adhesive sheet 210 isreduced in this portion. Thus, in the comparison of the thicknesses ofthe components, the thickness d1 of the adhesive sheet 210 is comparedto the other thicknesses.

According to the present invention, the logo 80 is provided in theposition overlapping the touch-panel flexible wiring substrate 50 butnot overlapping the touch panel 100. This makes it possible to prevent apeeling stress on the front window 200 and the touch panel 100. In otherwords, in FIG. 7, the distance L between an end portion of the secondlayer 82 of the logo 80, and an end portion of the touch panel 100 isset to be greater than zero.

With this configuration, even if the sum of the thickness of the logo80, and the thickness of the touch-panel flexible wiring substrate 50 isgreater than the thickness of the adhesive sheet 210, the touch-panelflexible wiring substrate 50 can move down, so that no peeling stress isapplied to the adhesive sheet 210. As a result, it is possible toachieve a highly reliable liquid crystal display device.

Second Embodiment

When the light from the light emitting diode of the backlight is inputto the logo 80 formed on the back side of the front window 200, apredetermined design quality may not be obtained in terms of the coloror other optical characteristics of the logo 80. In order to preventthis, in the first embodiment, the thickness of the second layer 82 ofthe logo 80 is increased. However, the light shielding effect may not besufficiently obtained in the first embodiment. In a second embodiment, athird layer 83, which is a light shielding film, is further formed onthe second layer 82 for forming white or a predetermined color of thelogo 80, in order to prevent the effect of the light from the lightemitting diode.

FIGS. 8A, 8B, and 8C are cross-sectional views of the process of formingthe logo 80 according to the second embodiment. FIG. 8A is a view inwhich the first layer 81 is formed on the back surface of the frontwindow 200. FIG. 8B is a view in which the second layer 82 is formed.FIG. 8C is a view in which the third layer 83 is formed. The thicknessof the first layer 81 is about 10 μm, and the thickness of the secondlayer 82 is about 10 μm. Similarly, the thickness of the third layer 83is about 10 μm.

In this embodiment, the thickness of the second layer 82 is smaller thanthe case of the first embodiment by the thickness of the third layer 83serving as a light shielding film formed on the second layer 82. Thesecond layer 82 is formed by a resin in which a pigment of white coloror a predetermined color is dispersed. The third layer 83, serving as alight shielding film, is black using an organic resin such as an epoxyresin in which the black pigment is dispersed.

In order to completely shield the light, the third layer 83 also coversa side portion of the second layer 82. In FIG. 8C, the total thicknessd2 from the first layer 81 to the third layer 83 is, for example, about30 μm. The thickness d2 of the logo 80 in FIG. 8C is important in therelationship between the thickness of the adhesive sheet 210 and thethickness of the touch-panel flexible wiring substrate 50.

FIG. 9 is a cross-sectional view in which the logo 80 of the threelayers is formed on the back surface of the front window 200. In FIG. 9,the thickness d1 of the adhesive sheet 210 is 100 μm, the thickness d3of the touch-panel flexible wiring substrate 50 is 70 μm, and thethickness d2 of the three layers of the logo 80 is 30 μm. Taking intoaccount the manufacturing tolerance of the components, the half isrepresented by d1<d2+d3.

In FIG. 9, an end portion of the third layer 83 of the logo 80 is formedon the outside of the end of the touch panel 100. In other words, L isgreater than zero in FIG. 9. Thus, the touch-panel flexible wiringsubstrate 50 can move down even if the relationship d1<d2+d3 isestablished. For this reason, no peeling stress is applied to theadhesive sheet 210 between the front window 200 and the touch panel 100.

In FIG. 9, L is the plane distance between the end portion of the secondlayer 82, and the end portion of the touch panel 100. In other words, Lrepresents the distance between the end portion of the three layers ofthe logo 80 and the end portion of the touch panel 100.

As described above, in the configuration of the second embodiment, evenif the logo 80 is formed of three layers, no peeling stress is appliedto the front window 200 and the touch-panel flexible wiring substrate50. As a result, it is possible to prevent the degradation of thereliability of the liquid crystal display device.

Third Embodiment

In the first embodiment, the distance L between the end portion of thesecond layer 82 of the logo 80 and the end portion of the touch panel100 is set to be greater than zero. In the second embodiment, thedistance L between the end portion of the three layers of the logo 80and the end portion of the touch panel 100 is set to be greater thanzero. In the vicinity of the distance L of zero, the bending stress islarge. If the relationship d1<d2+d3 is established in FIG. 7 and otherfigures, there may be a peeling stress on the adhesive sheet 210 betweenthe front window 200 and the touch-panel flexible wiring substrate 50.

A third embodiment deals with this problem. FIG. 10 is a detailedcross-sectional view around the logo 80 formed on the back surface ofthe front window 200 according to the third embodiment. In FIG. 10, theconfiguration below the touch panel 100 is omitted.

In FIG. 10, the touch-panel flexible wiring substrate 50 is mounted tothe touch panel 100. The touch-panel flexible wiring substrate 50 isprovided with a base material 52, a copper wiring 53 formed on the basematerial 52, and an overcoat 54 covering the copper wiring 53. Theovercoat 54 does not exist in the connecting portion of the touch-panelflexible wiring substrate 50 to the touch panel 100, but in which an Nilayer 55 and an Au layer 56 are formed.

The thicknesses of the individual components in FIG. 10 are as follows.The thickness of the base material 52 of the touch-panel flexible wiringsubstrate 50 is 40 μm. The thickness of the copper wiring 53 is 20 μm.The thickness of the overcoat 54 is 25 μm. The thickness of the Ni layer55 in a terminal portion is 1 to 5 μm, and the thickness of the Au layer56 is 0.03 to 0.3 μm. The Ni layer 55 and the Au layer 56 do not existin the portion in which the overcoat 54 is formed. In FIG. 10, d3represents the thickness of the touch-panel flexible wiring substrate 50in which the overcoat 54 does not exist. Here, the thickness d3 of thetouch-panel flexible wiring substrate 50 is compared to the thickness d1of the adhesive sheet 210, and to the thickness d2 of the logo 80.

In FIG. 10, the thickness of the logo 80 is the same as the case of thefirst embodiment. In other words, the thickness of the first layer 81 is10 μm, and the thickness of the second layer 82 thereof is 15 μm.Further, the thickness d1 of the adhesive sheet 210 is 100 μm. However,these components often vary in thickness. In FIG. 10, by setting L to0.3 μm or more, it is possible to suppress the peeling stress on theadhesive sheet 210 to a very small level even if the relationshipd1<d2+d3 is established.

In FIG. 10, when the distance M between an end portion of the overcoat54 of the touch-panel flexible wiring substrate 50 and an end portion ofthe touch panel 100 is extremely small, the bending stress on thetouch-panel flexible wiring substrate 50 increases. In this embodiment,however, the distance L between the end portion of the second layer 82of the logo 80 and the end portion of the touch panel 100 is set to 0.3mm or more, suppressing the bending stress on the touch-panel flexiblewiring substrate 50 to a small level. As a result, it is possible toprevent the peeling stress on the adhesive sheet 210 caused by thebending stress.

In FIG. 10, the description is given for the case in which the logo 80has two layers. However, this is the same for the logo 80 formed bythree layers as in the case of the second embodiment.

What is claimed is:
 1. A display device comprising: a front windowincluding a logo; a touch panel element which is bonded to the frontwindow; and a display panel, wherein the touch panel element and thefront window are bonded together with an adhesive material, wherein thelogo comprises a plurality of layers and is formed on a surface of thefront window, wherein a portion of the plurality of layers of the logois provided on a first portion of the surface of the front window whichis outside of a second portion of the surface of the front window whichis covered by the adhesive material, wherein the plurality of layers ofthe logo does not overlap the touch panel element in a plane view, andwherein the plurality of layers of the logo includes two color resin. 2.The display device according to claim 1, further including a flexiblewiring, wherein the flexible wiring is connected to a specific side ofthe touch panel, wherein, when a thickness of the adhesive material isd1, a thickness of the portion of the plurality of layers of the logo isd2, and a thickness of the flexible wiring substrate is d3, therelationship d1<d2+d3 is satisfied.
 3. The display device according toclaim 1, where a distance, in a plane view, between an end portion ofthe plurality of layers of the logo and an end portion of the touchpanel element is greater than 0.3 mm.
 4. A display device comprising: afront window including a logo; a touch panel element bonded to the frontwindow, and a display panel; wherein the touch panel element and thefront window are bonded together with an adhesive material, wherein aflexible wiring substrate is connected to a specific side of the touchpanel element, wherein the logo is formed on an inner surface of thefront window, which inner surface faces the touch panel element, whereinthe logo is formed by two layers including a first layer and a secondlayer, wherein a portion of the two layers of the logo is provided on afirst portion of the inner surface of the front window which is outsideof a second portion of the inner surface of the front window which iscovered by the adhesive material, wherein a distance, in a plane view,between an end portion of the second layer of the logo and an endportion of the touch panel element is greater than zero so that thesecond layer does not overlap the touch panel element in a plane view,and wherein a color of the first layer is different from that of thesecond layer.
 5. A display device comprising: a front window including alogo; a touch panel element bonded to the front window; and, a displaypanel, wherein a flexible wiring substrate is connected to a specificside of the touch panel element, wherein the logo is formed on an innersurface of the front window, which inner surface faces the touch panelelement, wherein the logo is formed by three layers including a firstlayer, a second layer, and a third layer, wherein an end portion of thesecond layer is covered by the third layer, wherein a portion of thethree layers of the logo is provided on a first portion of the innersurface of the front window which is outside of a second portion of theinner surface of the front window which is covered by the adhesivematerial, wherein a distance, in a plane view, between an end portion ofthe second layer of the logo and an end portion of the touch panelelement is greater than zero so that the second layer does not overlapthe touch panel element in a plane view, and wherein a color of thefirst layer is different from that of the second layer.